The invention relates to an energy storage arrangement with at least two rechargeable energy storage devices connected in parallel, wherein a first energy storage device includes a plurality of lead-based storage elements.
Energy storage systems having multiple parallel rechargeable energy storage devices are typically installed in modern motor vehicles, wherein a first energy storage is usually a lead-acid battery having several lead-based storage elements, also referred to as cells. A second energy storage device connected in parallel may be in the form of a capacitor, which generates, for example, the high currents required during starting of the motor vehicle. This is particularly advantageous when the high currents cannot be provided by the first energy storage device alone due to its low state of charge.
A fundamental problem with lead-based energy storage devices is the voltage drop as soon as a generator or battery charger from the power taken off or disconnected from the power grid. The voltage drop may in a typical lead-acid battery installed in a motor vehicle between a charging voltage of about 14 volts (V) during the charging process to a nominal voltage of about 12 volts amount when the charging current is removed. It is also disadvantageous with lead-based energy storage devices that they have a relatively low number of cycles, meaning that they can only be used for a comparatively small number of charging or discharging cycles. Both aspects have a negative impact on the overall performance of an energy storage arrangement based on lead-based energy storage devices. These problems equally apply to vehicles having a 24 volt onboard electrical system and vehicles having a 28 volt onboard electrical system, such as trucks or buses.